I'm not familiar with the wiper system but in looking at the Factory Service Manual looks like there is a combo relay (in the box behind the fuses), but I'm putting my money on the wiper switch itself being bad.

The relay you want to look at is at position 'H', which is in the front center of the relay box (front meaning closest to front of car). It's the biggest one in there. You can only see the 'H' once you pull the relay, as it is printed under it.

It also serves to control your turn signals, hazards and rear window defroster. Are you having problems with those too?

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-justin

1987 300TD, 1987 300TD
2008 R32, 2000 Passat Wagon